1. Field of the Invention
This invention relates to an ink cartridge for holding ink that is supplied to a recording head, that is removably attached to recording heads used in image forming apparatuses, and to an ink volume detection method for the ink cartridge.
2. Description of the Related Art
Conventionally, image forming apparatuses such as ink jet printers eject ink droplets from nozzles in a recording head mounted on a carriage, thereby recording images on recording media. The ejection of the ink droplets is accomplished by driving actuators such as electric-to-mechanical converter elements or electric-to-thermal converter elements positioned inside the recording head to generate pressure waves. The ink is supplied from an ink cartridge mounted on the recording head so that it can be easily removed and replaced. When air bubbles are mixed in with the ink liquid that is supplied from the ink cartridge, however, this has an adverse effect on the ejection of ink from the nozzles in the recording head.
In FIG. 20 is diagrammed an example of an ink cartridge structure as disclosed in Japanese Patent Application Laid-Open No. H9-70982/1997. An ink cartridge 150 has an ink supply hole 153 for supplying ink to a recording head 137, and an atmosphere connection hole 155 communicating to the outside atmosphere so as to allow air to flow in from outside the cartridge 150 as the ink volume is diminished by the consumption of ink absorbed in a porous material 152. Accordingly, after the ink cartridge 150 is filled with ink during fabrication, both of these openings (i.e. the ink supply hole 153 and atmosphere connection hole 155) are closed off by a sealing material. Also, as disclosed in Japanese Patent Application Laid-Open No. H7-132611/1995 (gazette), for example, at the time of shipment from the factory, the ink cartridge containing ink is sealed in a reduced-pressure condition inside a packaging bag to prevent ink leakage and the intrusion of air into the case prior to cartridge use. When it is time for use, the user removes the ink cartridge from the packaging bag, peels away the sealing material, thereby opening the atmosphere connection hole, and connects the ink supply hole to the recording head.
It is desirable to have the ink supply hole and the atmosphere connection hole located some distance apart in order both to prevent air from being drawn from the atmosphere connection hole into the ink supply hole via a short circuit and to facilitate use of the ink contained in the case without waste. For this reason, the ink supply hole and atmosphere connection hole are located on mutually opposing sides of the case, as diagrammed in FIG. 20. When filling the ink cartridge 150 with ink during the manufacturing process, on the other hand, the ink supply hole 153 serves also as the ink filling hole, and the atmosphere connection hole 155 is used as a pressure-reduction hole in order to reduce the pressure inside the case. Thus ink is filled in through the ink supply hole while effecting reduced pressure inside the case.
In the process of filling the ink cartridge 150 with ink, it is necessary to bring an ink filling apparatus and a pressure reduction apparatus up against both sides (the right side and left side in FIG. 20) of the ink cartridge 150. After the ink filling operation, sealing tape has been used to seal the ink supply hole 153 and the atmosphere connection hole 155. However, in the case of a cartridge structure such as that diagrammed in FIG. 20, the sealing tape must be pulled all the way around the case, from the upper surface (right side surface in FIG. 20) to the lower surface (left side surface in FIG. 20). Not only does this require a long length of tape, but, when the sealing tape is applied using a roller mechanism, the operation cannot be accomplished from one side of the case, so the sealing tape must be pulled around the case from the upper surface to the lower surface while rotating the case, thus involving an inefficient operation.
After sealing the ink filling hole (ink supply hole) with the sealing tape, the sealing tape has been heat welded by the application of heat. If the ink filling hole is wet with ink, however, heat welding cannot be adequately performed. When more heat is applied to avoid this, a problem arises in that the ink supply hole is deformed so that it cannot be properly connected to the recording head.
During the ink filling operation, moreover, when the interior of the case is placed under reduced pressure by the pressure reduction apparatus, the entire case is sometimes deformed, whereupon the case cannot be efficiently filled with ink.
When the configuration is such that a porous material 152 is accommodated inside the cartridge case to absorb the ink, as diagrammed in FIG. 20, it is demanded that the filling be done efficiently so that the ink reaches to the corners inside the porous material 152.
It is also demanded that, when the ink cartridge is being replaced, the user can easily peel away the sealing tape and efficiently utilize the ink in the case.
With this type of ink cartridge, furthermore, the remaining ink volume is continually or periodically detected by a detector installed in the recording apparatus. When it is detected that the remaining ink volume is low, the recording apparatus advises the user to replace the ink cartridge. This detection of the remaining ink quantity inside the ink cartridge is generally performed by detecting the ink liquid level. However, because the liquid level tends to shake and fluctuate because the ink cartridge is mounted on a carriage that moves in a sweeping motion in the width direction of the recording medium, erroneous detections often to occur. That being so, one measure known in the prior art for reducing the liquid level fluctuations (shaking) is that of providing rib-shaped members inside the cartridge case. This measure, however, requires the case structure to be complex. Also known is the method of directing light onto the porous material absorbing the ink inside the case and detecting the remaining ink quantity from the light reflected back. With this method, however, it is difficult to detect the remaining ink quantity accurately because the presence or absence of ink in the porous material differs from location to location therein.
In an ink jet type of image forming apparatus, in order to restore the ink ejection function, a suction cap connected to a suction pump is used to cover the recording head and suck out large amounts of ink from the recording head. When the ink liquid level inside the ink cartridge falls rapidly due to this suction, not all of the ink in contact with the wall surfaces of the ink cartridge moves instantly to the same height position, more or less, as the ink liquid level. Some of this ink remains adhering to the wall surfaces. This phenomenon becomes increasingly pronounced as the distance from the corners of the outer walls of the ink cartridge (i.e. the ridges thereof) increases, that is, the closer the center of the flat wall surfaces is approached. Accordingly, in cases where the detection site for a sensor is located near the center of the cartridge wall surface, even when the ink liquid level falls, so that there is little actual remaining ink quantity, that fact cannot be detected, wherefore erroneous detections occur, which is a problem.
When the remaining ink quantity inside the ink cartridge is being detected with a sensor, particularly one that is of the reflected light type, in order to accurately eject light onto a detection site from a light emitting element, and have the light reflected at the inner surface of the outer wall of the ink cartridge, that is the detection site received without failure by a light receiving element, the positions of the light emitting element and light receiving element relative to the detection site must be accurately established. However, the ink cartridge is made so that it can be freely attached to and detached from the recording head so that the user can replace it. The condition in which the ink cartridge is mounted will be slightly different, therefore, every time the user replaces it. In some cases, moreover, variation in the positions in which the reflected light sensors are attached relative to the carriage will arise at the stage of recording apparatus manufacture. Thus, when there are slight irregularities in the distance between the reflected light sensor and the detection site, or in the attachment position or angle of the reflected light sensor relative to the detection site, the light receiving element cannot properly detect the reflected light, so that the remaining ink quantity inside the ink cartridge cannot be detected or the remaining ink quantity detection precision sharply declines.
With this type of ink cartridge, furthermore, ink sometimes travels along the inner walls of the ink chamber holding the ink and reaches the atmosphere connection chamber adjacent to the ink chamber. This ink sometimes also passes through the atmosphere connection hole and leaks to the outside. If the case is transparent or semi-transparent, the case will become unsightly once ink penetrates into the atmosphere connection chamber. If the ink plugs up the atmosphere connection hole, that will impair the supply of ink to the recording head.
A type of ink cartridge is also known wherein, inside the ink cartridge case, a first chamber is provided for accommodating the porous material absorbing ink, and a second chamber is provided downstream from the first chamber, such that ink is supplied to the recording head via an ink supply hole from the second chamber. With such a structure as this, when air bubbles intrude into the second chamber from the first chamber, and those air bubbles are drawn to the recording head from the second chamber, there is a danger that the recording head will become incapable of ink ejection due to the air bubbles.
In a vacuum pack such as is described in the foregoing, furthermore, in order to maintain the interior thereof at reduced pressure for extended periods of time, it is necessary that there be space between the ink cartridge and the packaging bag of the pack, which space has a higher degree of vacuum than the interior of the ink cartridge. Supposing that a substantially rectangular ink cartridge is contained in a packaging bag, and that the packaging bag adheres tightly to the cartridge, outside air that gradually penetrates through the packaging bag will relatively quickly fill the slight gap between the packaging bag and the ink cartridge, making it difficult to maintain the reduced pressure condition for any extended period of time. Japanese Patent Application Laid-Open No. H10-250111/1998 discloses a cartridge wherein, in order to secure a prescribed volume for the reduced pressure space, the exterior shape is not made a simple rectangle but rather is made so that a part thereof projects, thus forming a space alongside the projecting part where the packaging bag does not tightly adhere. With this cartridge, holes are sometimes opened in the packaging bag by the cartridge corners. In Japanese Patent Application Laid-Open No. 7-132611, art is disclosed for inserting other components (spacers) inside the packaging bag such as corrugated cardboard or urethane foam which contain air internally and through which air readily passes. When separate components are inserted inside the packaging bag, however, the number of manufacturing processes increases, costs rise, and the exterior shape of the packaging bag becomes large, which is undesirable in the interest of smaller size.